A group III nitride semiconductor formed on a substrate has been used conventionally as a functional material for constituting a group III nitride semiconductor light emitting device having a pn junction structure such as a light emitting diode (LED) and a laser diode (LD) that irradiate short wavelength visible light (for example, refer to Patent Document 1). For example, in the LED emitting near ultraviolet light, blue light, or green light, n-type or p-type aluminum gallium nitride (compositional formula: AlXGaYN where 0≦X, Y≦1, and X+Y=1) is used to configure a cladding layer (for example, refer to Patent Document 2) and gallium indium nitride (compositional formula: GaYInZN where 0≦Y, Z≦1, and Y+Z=1) is used to configure a light emitting layer (for example, refer to Patent Document 3).
In addition, a group III nitride semiconductor in which impurities such as silicon (Si) are doped is arranged in between the substrate and the light emitting layer and is used for controlling resistance.
Incidentally, since a sapphire substrate that is most widely used as a substrate constituting a group III nitride semiconductor light emitting device is an insulator and thus has a disadvantage of having low thermal conductivity, there is a demand for the development of substrates to serve as an alternative to the sapphire substrate. As an alternative substrate for the sapphire substrate, the use of a substrate that has high electrical and thermal conductivity and is composed of a group III nitride semiconductor crystal having the same crystal lattice constant as that of a group III nitride semiconductor has currently been proposed.
In addition, apart from the abovementioned substrate composed of the group III nitride semiconductor crystal, a substrate in which a group III nitride semiconductor layer is laminated on a base composed of a hetero substrate containing sapphire has been proposed as an alternative substrate for the sapphire substrate. In such a substrate, a laminated structure that serves as an LED is generally formed on the group III nitride semiconductor layer, which is laminated on the hetero substrate. Such a substrate is advantageous when different methods are used for growing crystals to produce the group III nitride semiconductor layer on the hetero substrate and for growing crystals to form the laminated structure that serves as an LED. In general, the hydride vapor phase epitaxy (HVPE) method, the molecular beam epitaxy (MBE) method, and the like are used as a method for forming the group III nitride semiconductor layer and the metalorganic chemical vapor deposition (MOCVD) method and the like are used for forming the laminated structure.
In addition, the substrate having the group III nitride semiconductor layer laminated therein will be electrically conductive when a hetero substrate composed of Si and ZnO is used as a base. For this reason, it is possible to configure a group III nitride semiconductor light emitting device having a double sided electrode structure, in which an electric current is conducted through the device in the vertical direction, by producing electrodes on both faces of the semiconductor light emitting device.
In addition, even when an insulating substrate such as a sapphire substrate is used as a base in the substrate having the group III nitride semiconductor layer laminated therein, it is possible to achieve a group III nitride semiconductor light emitting device having a double sided electrode structure by employing a technique to remove the sapphire substrate before forming the electrodes.    [Patent Document 1] Japanese Unexamined Patent Application, First Publication No. 2000-332364    [Patent Document 2] Japanese Unexamined Patent Application, First Publication No. 2003-229645    [Patent Document 3] Japanese Examined Patent Application, Second Publication No. Sho 55-3834